1. Technical Field of the Invention
This invention relates to a shaft coupling comprising a pair of complementally shaped, detachably joinable coupling sleeve halves which form, when they are joined together, a split coupling sleeve having an axis and provided with at least one seat for a first shaft member which is to be non-rotatably connected with a second shaft member so that the first and second shaft members are centred on said axis of the coupling sleeve, clamping elements for holding the coupling sleeve halves together and clamping them about the first shaft member, and a retaining device including interengaging retaining elements for positively locking the first shaft member against rotational movement relative to the coupling sleeve.
2. Prior Art
In known shaft couplings of this kind, also known as split clamping or compression couplings, the retaining device usually comprises a keyed joint having at least one axial key received in registering keyways in the coupling sleeve formed by the coupling sleeve halves and in the shaft member or members. The key serves as a positively locking member to prevent relative rotational movement of the coupling sleeve on the one hand and the shaft member or members on the other hand if the frictional locking of the shaft member or members to the coupling sleeve should be inadequate. Sometimes, the retaining device also comprises one or more additional retaining elements providing a positive locking of the shaft member or members to the coupling sleeve against axial movement relative to the coupling sleeve.
Split clamping couplings have several advantages. For example, they are inexpensive in comparison with many other couplings. They do not require special tools for their installation and also do not require any extra length of the shafts to enable the installation. In prior art split clamping couplings the retaining device is problematic, however.
A retaining device comprising axial keys as locking members has important disadvantages. One disadvantage is that the keyways form stress concentration areas in the coupling sleeve and in the shaft member or members and therefore limit the torque that can be transmitted.
Another disadvantage is that if the coupling and the shaft member or members have to be positively held together both rotationally and axially to be able to transmit high torques and great axial forces, a retaining device including both at least one axial key and at least one transverse key is required.
A further disadvantage is that it is often difficult to provide an adequate clamping force, that is, adequate friction between the coupling sleeve and the shaft member or members, especially in split clamping couplings which are required to transmit very high torques. As a practical matter, it is therefore necessary to rely on the retaining device for the transmission of at least a portion of the desired torque.
A disadvantage is also that the keyed joints often exhibit a certain rotational play that has undesired effects when the direction of the torque is repeatedly reversed.
Still another problem is that the contact surfaces between the coupling sleeve and the shaft member or members are prone to so-called fretting or chafing corrosion.